Active matrix type display device and method of manufacturing the same

ABSTRACT

A method of manufacturing an active matrix type display device, which is reliable and flexible, is provided. An active matrix type display device according to an aspect of the present invention includes: a first substrate, which is flexible; a thin glass layer provided on the first substrate via an adhesion layer, and having projections and depressions on a surface thereof opposing to the first substrate, the projections and depressions having rounded tips and bottoms; active elements provided on the thin glass layer, each active element corresponding to a pixel; a display provided above the thin glass layer, and driven by the active elements to display an image pixel by pixel; and a second substrate provided on the display, and having an opposing electrode formed thereon.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2002-142373, filed on May17, 2002 in Japan, the entire contents of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an active matrix type displaydevice and a method of manufacturing the same.

[0004] 2. Related Art

[0005] In an active matrix type display device, which is widely used atpresent, a highly heat-resistant substrate, e.g., a non-alkali glasssubstrate, is used as a substrate on which devices are formed during anactive element forming process, and the highly heat-resistant substrateis continuously used as a supporting substrate of the display device.

[0006] When a thin film transistor is formed by using a polycrystallinesilicon layer as a semiconductor layer in which a channel region isformed, the following procedure is employed, taking into considerationthe processing temperature etc. at the time of forming each functionalfilm.

[0007] First, a barrier layer is formed on a device forming substrate ofnon-alkali glass so that the minor constituent of the glass does notseep therefrom. Then, an amorphous silicon layer is formed thereon.Subsequently, a short-time local heat treatment using an eximer laser isperformed on the workpiece so that the amorphous silicon layer becomes apolycrystalline silicon layer through the solid phase or liquid phasegrowth. Thereafter, the thus obtained polycrystalline silicon layer isshaped. Subsequently, a thin film to serve as a gate insulating film isdeposited, and then a metal layer, on which a gate electrode and a gatewiring are formed, is formed and shaped. Furthermore, an ionimplantation is performed using the gate electrode as a mask through theion doping method in order to form a source and drain regions in thepolycrystalline silicon layer. Then, a thermal processing is performedto activate ions. Accordingly, a channel region and a source and drainregions are formed in the polycrystalline silicon layer. Subsequently,an interlayer dielectric film is formed to isolate the signal lines etc.and the gate lines, and then contact holes to the source and drainregions are formed. Then, a metal layer is formed and shaped to make asource and drain electrodes, to form a thin film transistor and wirings.When an active matrix type liquid crystal display device is formed, thedevice forming substrate, on which the active elements are formed, iscontinuously used as a supporting substrate.

[0008] When a display device having a curved display surface should bemanufactured, a light and flexible substrate, such as a plasticsubstrate, is used as a supporting substrate. Such a light and flexiblesubstrate is preferable as a supporting substrate of a display deviceused in a mobile information terminal. However, since such a plasticsubstrate does not have a sufficient heat-resistance or a sufficientdimensional stability, it is not possible to use such a plasticsubstrate as a device forming substrate on which active elements ofpolycrystalline silicon, which are superior in switching properties, areformed, and to continuously use the plastic substrate as a supportingsubstrate. Accordingly, a method is employed, in which active elementsare formed on a device forming substrate of glass, etc., which is highlyresistant to a high temperature process, and then the active elementsare transferred to a light and flexible supporting substrate formed of,e.g., a plastic. More specifically, active elements are formed on adevice forming substrate of glass, the side on which the active elementsare formed is bonded to a temporary substrate. Then, the device formingsubstrate is removed by the etching, etc., and the active elements aretransferred to a final supporting substrate.

[0009] In the above-described method, however, the process of formingactive elements and their wirings on a device forming substrate, whichis superior in heat resistance, and then transferring them to, e.g., aplastic substrate, has a problem in the way of removing the deviceforming substrate used to form the active elements.

[0010] For example, in the case where the device forming substrate usedto form the active elements should be completely removed, it isdifficult to etch the device forming substrate without damaging theactive elements on the device forming substrate.

[0011] With respect to the case where it is not necessary to completelyremove the device forming substrate used to form the active elements,the present inventors have developed a display device in which thethickness of a supporting substrate of glass, on which active elementsare formed, is reduced, and then the glass substrate is bonded to aflexible sheet via an adhesion layer (for example, see Japanese PatentApplication No. 2002-84924). In this display device, if the flexiblesheet is bent to form a curved display, it may be possible that theglass substrate breaks. Therefore, this display device is not reliablewhen used in a curved application.

[0012] As described above, it has been difficult to obtain a reliableand flexible display device without damaging the active matrix devicesby first forming active matrix devices and their wirings on a highlyheat-resistant device forming substrate, and then transferring them to aflexible plastic substrate.

SUMMARY OF THE INVENTION

[0013] An active matrix type display device according to a first aspectof the present invention includes: a first substrate, which is flexible;a thin glass layer provided on the first substrate via an adhesionlayer, and having projections and depressions on a surface thereofopposing to the first substrate, the projections and depressions havingrounded tips and bottoms; active elements provided on the thin glasslayer, each active element corresponding to a pixel; a display providedabove the thin glass layer, and driven by the active elements to displayan image pixel by pixel; and a second substrate provided on the display,and having an opposing electrode formed thereon.

[0014] An active matrix type display device according to a second aspectof the present invention includes: a first substrate, which is flexible;a thin glass layer provided on the first substrate via an adhesionlayer; active elements provided on the thin glass layer, each activeelement corresponding to a pixel; a display provided above the thinglass layer, and driven by the active elements to display an image pixelby pixel; and a second substrate provided on the display, and having anopposing electrode formed thereon, a thickness of the thin glass layerin regions corresponding to the active elements being thicker than athickness of other regions.

[0015] An active matrix type display device according to a third aspectof the present invention includes: a first substrate, which is flexible;a thin glass layer provided on the first substrate via an adhesionlayer; a compressive stress applying layer provided between the adhesionlayer and the thin glass layer, the compressive stress applying layerapplying a compressive stress to a surface of the thin glass layer at aside of the adhesion layer; active elements provided on the thin glasslayer, each active element corresponding to a pixel; a display providedabove the thin glass layer, and driven by the active elements to displayan image pixel by pixel; and a second substrate provided on the display,and having an opposing electrode formed thereon.

[0016] An active matrix type display device according to a fourth aspectof the present invention includes: a first substrate, which is flexible;a thin glass layer provided on the first substrate via an adhesionlayer; a hydroxyl group blocking layer provided between the adhesionlayer and the thin glass layer, and blocking a soakage of a hydroxylgroup; active elements provided on the thin glass layer, each activeelement corresponding to a pixel; a display provided above the thinglass layer, and driven by the active elements to display an image pixelby pixel; and a opposing substrate provided on the display.

[0017] An active matrix type display device according to a fifth aspectof the present invention includes: a first substrate, which is flexible;a thin glass layer provided on the first substrate via an adhesionlayer; active elements provided on the thin glass layer, each activeelement corresponding to a pixel; a display provided above the thinglass layer, and driven by the active elements to display an image pixelby pixel; a second substrate provided on the display, and having anopposing electrode formed thereon; and a reinforcing member having amesh structure, provided in the adhesion layer.

[0018] A method of manufacturing an active matrix type display deviceaccording to a sixth aspect of the present invention includes: formingactive elements each corresponding to a pixel on a device formingsubstrate of glass; polishing the device forming substrate to make itthinner by first performing a mechanical polishing, and then performinga chemical polishing; bonding a surface of the device forming substrate,which has been polished, to a plastic substrate via an adhesion layer;and forming a display driven by the active elements to display an imagepixel by pixel, by placing a counter substrate so as to oppose to thedevice forming substrate.

[0019] A method of manufacturing an active matrix type display deviceaccording to a seventh aspect of the present invention includes: formingactive elements each corresponding to a pixel on a device formingsubstrate of glass; polishing the device forming substrate to make itthinner; forming a compressive stress applying layer on a polishedsurface of the device forming substrate, a coefficient of linearexpansion of the compressive stress applying layer being larger than acoefficient of linear expansion of the device forming substrate, andthen cooling the compressive stress applying layer; bonding a plasticsubstrate to a surface of the device forming layer, on which thecompressive stress applying layer is formed; and forming a displaydriven by the active elements to display an image pixel by pixel, byplacing a counter substrate so as to oppose to the device formingsubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIGS. 1A and 1B show an active matrix type display deviceaccording to the first embodiment of the present invention, of whichFIG. 1A is a plan view and FIG. 1B is a sectional view taken on lineA-A′ of FIG. 1A.

[0021]FIG. 2 is a sectional view showing a step of a method of formingan active element of the active matrix type display device according tothe first embodiment of the present invention.

[0022]FIG. 3 is a sectional view showing a step of the method of formingan active element of the active matrix type display device according tothe first embodiment of the present invention.

[0023]FIG. 4 is a sectional view showing a step of the method of formingan active element of the active matrix type display device according tothe first embodiment of the present invention.

[0024]FIG. 5 is a sectional view showing a step of the method of formingan active element of the active matrix type display device according tothe first embodiment of the present invention.

[0025]FIG. 6 is a sectional view showing a step of the method of formingan active element of the active matrix type display device according tothe first embodiment of the present invention.

[0026]FIG. 7 is a sectional view showing a step of a method oftransferring the active element of the active matrix type display deviceaccording to the first embodiment of the present invention.

[0027]FIG. 8 is a sectional view showing a step of the method oftransferring the active element of the active matrix type display deviceaccording to the first embodiment of the present invention.

[0028]FIG. 9 is a sectional view showing a step of the method oftransferring the active element of the active matrix type display deviceaccording to the first embodiment of the present invention.

[0029]FIG. 10 is a sectional view showing a step of the method oftransferring the active element of the active matrix type display deviceaccording to the first embodiment of the present invention.

[0030]FIG. 11 is a sectional view schematically showing a thin glasslayer after being subjected to a mechanical polishing step.

[0031]FIG. 12 is a sectional view schematically showing a thin glasslayer after being subjected to a chemical polishing step performed aftera mechanical polishing step.

[0032]FIG. 13 is a sectional view showing a thin glass layer with somecracks left, which is obtained by performing a mechanical polishing on aglass substrate.

[0033]FIG. 14 is a sectional view showing a thin glass layer with somecracks left, which is obtained by performing a mechanical polishing on aglass substrate.

[0034]FIG. 15 is a sectional view showing a thin glass layer with somecracks left, which is obtained by performing a mechanical polishing on aglass substrate.

[0035]FIG. 16 is a sectional view for explaining stress relaxation dueto the projections and depressions of a thin glass layer.

[0036]FIG. 17 is a sectional view for explaining stress relaxation dueto the projections and depressions of a thin glass layer.

[0037]FIG. 18 is a sectional view for explaining stress relaxation dueto the projections and depressions of a thin glass layer.

[0038]FIG. 19 is a sectional view showing an active matrix displaydevice according to the second embodiment of the present invention.

[0039]FIG. 20 is a sectional view showing a step of a method ofmanufacturing the active matrix type display device according to thesecond embodiment of the present invention.

[0040]FIG. 21 is a sectional view showing a step of the method ofmanufacturing the active matrix type display device according to thesecond embodiment of the present invention.

[0041]FIG. 22 is a sectional view showing a step of the method ofmanufacturing the active matrix type display device according to thesecond embodiment of the present invention.

[0042]FIG. 23 is a sectional view showing a step of the method ofmanufacturing the active matrix type display device according to thesecond embodiment of the present invention.

[0043]FIG. 24 is a sectional view showing an active matrix type displaydevice according to the third embodiment of the present invention.

[0044]FIG. 25 is a sectional view for explaining the status of stressapplied to a normal glass substrate.

[0045]FIG. 26 is a sectional view for explaining the status of stressapplied to a thin glass layer obtained by reducing the thickness of anormal glass substrate.

[0046]FIG. 27 is a sectional view showing a step of a method ofmanufacturing the active matrix type display device according to thethird embodiment of the present invention.

[0047]FIG. 28 is a sectional view showing a step of the method ofmanufacturing the active matrix type display device according to thethird embodiment of the present invention.

[0048]FIG. 29 is a sectional view showing a step of a method ofmanufacturing the active matrix type display device according to thethird embodiment of the present invention.

[0049]FIG. 30 is a sectional view showing an active matrix type displaydevice according to the fourth embodiment of the present invention.

[0050]FIG. 31 shows a chemical formula of a silane coupling agent.

[0051]FIG. 32 is a sectional view showing an active matrix type displaydevice according to the fifth embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0052] Embodiments of the present invention are intended to give aflexibility and a strength to an active matrix type display deviceobtained by first forming active elements on a glass substrate servingas a device forming substrate, then making the glass substrate thinner,and then bonding the glass substrate to a flexible supporting substrate,which can be bent, such as a plastic substrate, via an adhesion layer.

[0053] The mechanical properties of a glass substrate with a thicknessof as thin as a few tens of Dm (thin glass layer) are not away from themechanical properties of glass. The softness and the flexural strengthof the glass are dependent on the Griffith's crack theory relating tothe brittle fractures caused by cracks existing in the surface area. Ifthere are cracks, the physical property value of, e.g., the flexuralstrength of glass decreases to about {fraction (1/10)} or less of thatof an ideal glass surface that does not have any crack. Accordingly, itis possible to improve the flexibility and the reliability of an activematrix type display device by introducing a structure for preventing thedevelopment of cracks existing in the surface of a thin glass layer. Inthe present invention, the following means are employed to prevent thedevelopment of cracks existing in the surface of the thin glass layercontacting the adhesion layer.

[0054] First, the thickness of a surface of the thin glass layer, whichis bonded to the plastic substrate, is shaped to have gentle projectionsand depressions having a height of a fiftieth or more and a half or lessof the thickness of the thin glass layer. This can be achieved by firstmechanically polishing the glass substrate, and then chemicallypolishing the surface of the glass substrate, so that the tips andbottoms of the projections and depressions are rounded. Further, due tothe above-described chemical polishing, the angled portions at the tipsof the cracks can be rounded. Subsequently, the surface of the thinglass layer to be bonded to the plastic substrate is shaped to have awaveform shape, thereby preventing the overconcentration of the tensilestress to the cracks.

[0055] Second, the thickness of the thin glass layer is adjusted so thatthe areas including the devices such as active elements and wiringsconstituting the active matrix become thicker, and the other areasbecome thinner. The reason for such adjustment is that the areas of theglass substrate, on which active elements constituting the active matrixare formed, receive a relatively large residual stress, resulting inthat the strength of those areas decreases. In order to solve thisproblem, the thickness of the areas including the active elements isincreased to improve the strength.

[0056] Third, a compressive stress is applied to a surface of the thinglass layer, which is bonded to the plastic substrate. Generally, acrack of glass develops when a tensile stress is applied to the tipthereof. Accordingly, a compressive stress is generally applied to thesurface of a glass substrate so as to prevent the development of cracks.However, since a thin glass layer is formed by polishing a deviceforming substrate, the inside area of the glass, to which the tensilestress is applied, is exposed. Accordingly, cracks are easy to develop.Therefore, if a compressive stress is applied to the polished surface ofthe thin glass layer in the initial state, when the entire active matrixtype display device is bent so as to apply a tensile stress to thepolished surface of the thin glass layer, it is possible to prevent thedevelopment of cracks. The compressive stress is applied by forming acompressive stress applying layer on the polished surface of the thinglass layer by the use of a material having a higher coefficient oflinear expansion than glass, and by cooling it so as to apply acompressive stress inside the surface of the thin glass layer.

[0057] Fourth, a hydroxyl group blocking layer for blocking moleculeshaving hydroxyl groups, such as moisture, is formed on the surface ofthe thin glass layer, which is to be bonded to the plastic substrate. Itis known that hydroxyl radicals advance the development of cracks inglass. Since the thin glass layer of the active matrix type displaydevice according to the embodiments of the present invention is formedby polishing the device forming substrate, which eliminates theinitially applied compressive stress, it is possible to prevent thedevelopment of cracks in the thin glass layer by providing a layer ofpreventing the development of cracks between the thin glass layer andthe adhesion layer.

[0058] Fifth, a reinforcing member having a mesh structure is providedinside the adhesion layer. Preferably, this reinforcing member isprovided inside the adhesion layer directly below the areas on which theactive elements are formed. With the reinforcing member, it is possibleto reinforce the thin glass layer at the portions on which the activeelements are formed, and which have a relatively large residual stressleading to the decrease in strength. Accordingly, it is possible toconsiderably improve the strength of the glass layer.

[0059] Hereinafter, the embodiments of the present invention will bedescribed with reference to the accompanying drawings. It should benoted that the present invention is not limited to the followingembodiments.

[0060] (First Embodiment)

[0061] The first embodiment of the present invention will be describedbelow. FIGS. 1A and 1B show an active matrix type display device in thisembodiment. FIG. 1A is a plan view, and FIG. 1B is a sectional viewtaken on line A-A′ of FIG. 1A. FIGS. 2 to 6 are sectional views showingthe steps of forming an active element of the active matrix type displaydevice of this embodiment. FIGS. 7 to 10 are sectional views showing thetransfer process of the active matrix type display device of thisembodiment. It should be noted that although 2×2 devices are shown inFIG. 1A, two devices are shown in FIGS. 1B and 7-10, and one device isshown in FIGS. 2-6, actually a great number of such devices are arrangedin a two dimensional array.

[0062] In this embodiment, active elements are formed by using a glasssubstrate as a device forming substrate; the device forming substrate isfirst mechanically polished, and then chemically polished, therebymaking a thin glass layer having projections and depressions with aheight of a fiftieth or more and a half or less of the thickness of thethin glass layer; and the active matrix type display device is completedwith thus obtained thin glass layer. In other words, the strength of thethin glass layer is improved by changing the shape of the polishedsurface of the thin glass layer after being subjected to the mechanicalpolishing from a sharp shape to a rounded shape by the chemicalpolishing. Here, the height of the projections and depressions means themaximum length from a tip of a projection to a bottom of a depression.

[0063] As shown in FIGS. 1A and 1B, the active matrix type displaydevice of this embodiment includes a plastic substrate 101, a thin glasslayer 103, which is located on the plastic substrate 101 via an adhesionlayer 102, an undercoat layer 104 located on the thin glass layer 103,thin film transistors (active elements) 105, each corresponding to apixel, and located on the undercoat layer 104, a liquid crystal layer(optical valve elements) 106 located above the thin glass layer 103, anddriven by the thin film transistors 105 to display an image pixel bypixel, and an opposing substrate 108 having an opposing electrode 107and located on the liquid crystal layer 106. The thin glass layer 103has projections and depressions having a height of a fiftieth or moreand a half or less of the thickness of the thin glass layer 103 on thesurface opposing to the plastic substrate 101.

[0064] Each active element 105 includes an active layer 110, which isformed like an island, a gate insulating layer 111 formed all over theactive layer 110, a gate electrode 112 formed on the gate insulatinglayer 111 in a region corresponding to the active layer 110, aninterlayer dielectric film 113 formed all over the gate electrode 112,and a source and drain electrodes 114 each connected to the active layer110 via a contact hole formed through the gate insulating layer 111 andthe interlayer dielectric film 113. One of the source and drainelectrodes 114 is connected to a pixel electrode 115.

[0065] Next, a method of manufacturing an active element of the activematrix type display device according to this embodiment will bedescribed with reference to FIGS. 2 to 6.

[0066] First, as shown in FIG. 2, the undercoat layer 104 of siliconoxide or silicon nitride is deposited on a non-alkali glass substrate(device forming substrate) 201, which has been sufficiently cleaned,through the plasma enhanced chemical vapor deposition (PECVD) method,etc., using a material such as silane. With the undercoat layer 104, itis possible to prevent the trace of alkali elements from seeping fromthe glass substrate 201.

[0067] Then, the active layer 110 is formed by first growing anamorphous-silicon layer through the PECVD method, etc., and theninstantaneously melting it by irradiating it with an excimer laser usingKrF, etc., to make a polycrystalline silicon layer. Then, the thusobtained polycrystalline silicon layer is isolated through theanistropic etching method using the reactive ion etching (RIE) method bythe use of a fluorine gas.

[0068] Subsequently, the gate insulating layer 111 of silicon oxide orsilicon nitride is formed through the PECVD method so as to cover theactive layer 110, as shown in FIG. 3.

[0069] Next, the gate electrode 112 is formed. First, a metal layer ofMo, W, Ta, or an alloy thereof, is deposited on the gate insulatinglayer 111 using the sputtering method, etc. A photoresist is applied tothe metal layer. Then, a resist pattern is formed by using thephotolithography method. Finally, the gate insulating layer 112, theshape of which corresponds to that of the active layer 110, and gatelines 202 having predetermined shapes are formed by selectively removingthe metal layer in the areas that do not have resist patterns by soakingthe workpiece in a solvent.

[0070] Then, as shown in FIG. 4, an impurity is implanted to the activelayer 110 so as to form a contact surface in a region to contact to asource and drain electrodes, which will be described layer. In thisembodiment, phosphorous (P) is used as the impurity. As shown by arrowsin FIG. 4, the impurity is implanted by using the gate electrode 112 asa mask through the ion doping method with the ion concentration of about10²² cm⁻³. Subsequently, a thermal treatment is performed to activatethe implanted phosphorous.

[0071] Next, as shown in FIG. 5, a silicon oxide layer or a siliconnitride layer to serve as an interlayer dielectric film 113 is grown tocover the gate electrode 112 and the gate lines 202 through theatmosphere pressure chemical vapor deposition (APCVD) method. Then, athrough-hole for the source and drain electrodes to contact the activelayer 110 is formed through the interlayer dielectric film 113 and thegate insulating layer 111 through the photo-etching process.

[0072] Subsequently, as shown in FIG. 6, a metal such as Mo, Ta, W, Al,Ni, etc., or an alloy thereof, or layers thereof, is (are) deposited onthe interlayer dielectric film 113 so as to connect to the active layer110 via the through-hole. Then, a source and drain electrodes 114 andsignal lines 203 are formed through the same photo-etching process asthat used to form the gate electrode. One of the source and drainelectrodes 114 is connected to the pixel electrode 115.

[0073] In this thin film transistor and wiring forming process, athermal treatment at a temperature of, e.g., 500° C. or more should beperformed. Since the device forming substrate of this embodiment is anon-alkali glass substrate which is widely used to manufacture amorphoussilicon thin film transistors and polycrystalline silicon thin filmtransistors, and the thickness thereof is the same level as that used tomanufacture amorphous silicon thin film transistors and polycrystallinesilicon thin film transistors, there is no problem in manufacturing thinfilm transistors and wirings of this embodiment at such a temperature.In addition, when polycrystalline silicon thin film transistors aremanufactured, it is possible to employ the conventional fabricatingmethod.

[0074] Next, a method of manufacturing an active matrix type displaydevice of this embodiment, after the active elements are formed, will bedescribed with reference to FIGS. 7-10, in which the details of thinfilm transistors are omitted.

[0075] As shown in FIG. 7, the surface of the glass substrate 201, onwhich the thin film transistors 105 are formed, is coated, without anyspace, with an adhesive agent, which is superior in hydrofluoric acidproperties, and the adhesion power of which is weakened if it isirradiated with an ultraviolet light, so as to form a temporary adhesionlayer 204. Further, a temporary substrate 205 of a fluoroplastic sheet,which is highly resistant to hydrofluoric acid, is provided on thetemporary adhesion layer 204 so as to support to the glass substrate201. The adhesion surface of the temporary substrate 205 is coated so asto improve the adhesion properties thereof with respect to an organicmaterial.

[0076] As shown in FIG. 8, the glass substrate 201 is mechanicallypolished using a polishing agent, with the level of coarseness of thepolishing agent being adjusted, so that the thickness thereof becomesabout 0.1 mm. In this way, the glass substrate 201 becomes the thinglass layer 103.

[0077] As shown in FIG. 9, after the mechanical polishing step, theentire workpiece is soaked in a hydrofluoric acid solvent so as tochemically polish the workpiece. In this way, the thickness of the thinglass layer 103 becomes about 30 μm. At this time, it is preferable thatafter the thickness of the thin glass layer 103 reaches a predeterminedlevel, ammonia, for example, is added to the hydrofluoric acid solventso as to adjust the etching rate.

[0078] It is preferable that the height of the projections anddepressions of the thin glass layer is one fiftieth or more and one halfor less of the thickness of the thin glass layer. If the height is lessthan one fifties of the thickness, the surface becomes substantially thesame state as the surface of mirror. Therefore, the effect of stressrelaxation cannot be expected. If the height is more than a half of thethickness, the internal stress of the glass is concentrated on thedepressed portions. If the height is one twenties or more and a half orless of the thickness, the contact area between the thin glass layer 103and the adhesion layer is increased, resulting in that it is possible toobtain a good adhesion properties.

[0079] It is preferable that the thickness of the thin glass layer 103is about 5 □m or more in order to maintain the strength, and about 100□m or less in order to keep it light. Further, in order to make theheight of the projections and depressions of the thin glass layer 103 inthe range of a fifties to a half of the thickness of the thin glasslayer 103, the grain size (coarseness) of the polishing agent such as agrind stone is adjusted to have substantially the same size as theheight of the projections and depressions to be made. For example,assuming that the thickness of the thin glass layer 103 is about 50 □m,and the height of the projections and depressions should be about atenth of the thickness, a grind stone having a grain size of about 5 μmcan be used.

[0080] As shown in FIG. 10, an adhesion layer 102 is formed all over theetched surface of the thin glass layer 103 after the thin glass layer103 is fully cleaned. Then, a polyether sulfone (PES) film having athickness of about 0.1 mm serving as a plastic substrate 101 is bondedto the adhesion layer 102 using the vacuum laminating technique.

[0081] Thereafter, the workpiece is irradiated with an ultraviolet lightfrom the temporary substrate 205 side, thereby weakening the adhesionpower of the temporary adhesion layer 204. Then, the intermediatesubstrate 205, together with the adhesion layer 204, is slowly peeled toexpose the surface of the thin film transistor 105 such as theinterlayer dielectric film 113. The constituent elements of thetemporary adhesion layer 204, which may remain on the workpiece, areremoved through the organic cleaning method using isopropanol, etc.Although the interlayer dielectric film 113 is exposed in thisembodiment, the present invention is not limited to such a structure.For example, a protection layer of a novolac resin can be providedbetween the thin film transistors 105 and the temporary adhesion layer204 so as to protect the thin film transistors 105. The scope of theselection of the material of the temporary adhesion layer 204 can beexpanded by providing a protection layer.

[0082] Thereafter, the completed active matrix substrate and theopposing substrate 108, on which the opposing electrode 107 is formed,are combined to form a cell. Then, liquid crystal is injected therein toform the liquid crystal layer 106. Subsequently, the workpiece is sealedto complete the active-matrix type display device of this embodiment.

[0083] Next, the glass substrate polishing step in the method ofmanufacturing an active matrix type display device in this embodimentwill be described below.

[0084] In this embodiment, both the mechanical polishing step and thechemical polishing step are employed in the glass substrate polishingstep. FIG. 11 schematically shows the thin glass layer 103 after beingsubjected to the mechanical polishing step, and FIG. 12 schematicallyshows the thin glass layer 103 after being subjected to the chemicalpolishing step that follows the mechanical polishing step. In thedrawings, the lower side is the polished side. As shown in FIG. 11,there are a lot of sharp cracks 301 on the polished surface of the thinglass layer 103 after being subjected to the mechanical polishing step.Such cracks are formed by the polishing agent used in the mechanicalpolishing. Normally, the coarseness of the polishing agent is changedfrom the coarse to fine, e.g., #500, #1,000, #3,000, . . . in order toimprove the smoothness of the polished surface. However, if a long timeis taken to perform the mechanical polishing in such a manner, theproductivity is deteriorated. In addition, it is difficult to know thestatus of the cracks and flows on the side opposite to the side on whichthe thin film transistors are formed. Accordingly, it is possible that acrack which may deteriorate the strength of the glass may be left.

[0085] Accordingly, in this embodiment, a chemical polishing isperformed on the workpiece as shown in FIG. 11 to form a wavy structureas shown in FIG. 12, with the projections and depressions 302 having aheight of a fifth or more and a half or less of the thickness of thethin glass layer 103. The wavy structure does not include any sharpedge. Thus, according to this embodiment, it is possible to obtain astrong thin glass layer without spending a long time for the mechanicalpolishing.

[0086] FIGS. 13-15 schematically shows the case where the thin glasslayer after being subjected to the mechanical polishing has cracks. Inthe drawings, the lower side is the polished side. If there is a crack301 developed from a flaw, which has not removed during the polishing ofthe thin glass layer 103, or which has been caused during the subsequentstep, as shown in FIG. 13, the strength of the thin glass layer 103 maybe weakened due to the existence of the crack 301.

[0087] If the entire display device (not shown) including the thin glasslayer 103 is bent in the direction shown by solid line arrows in FIG.14, a compressive stress is applied to the polished surface of the thinglass layer 103, while a tensile stress is applied to the surfaceopposing to the polished surface. Since a compressive stress in thedirection of broken line arrows is applied to the crack 301, the crack301 does not develop further.

[0088] However, if the entire display device (not shown) is bent in thedirection shown by solid line arrows in FIG. 15, a tensile stress isapplied to the polished surface of the thin glass layer 103, while acompressive stress is applied to the surface opposing to the polishedsurface. Accordingly, a tensile stress is intensively applied to the tipof the crack 301 as shown by broken line arrows. The flatter thepolished surface of the thin glass layer is, and the fewer the number ofcracks is, i.e., the better the fabrication condition is, the moreintensively the stress is applied to the tips of the few cracks, therebyeasily damaging the glass.

[0089] In the case where the wavy structure according to this embodimentis employed in the polished surface of the thin glass layer, regardlessof the direction in which the entire display device including the thinglass layer is bent, the possibility of causing damage thereto is low.The reason is that there is no crack having a sharp tip because of thesufficient chemical polishing, which makes the tips of the cracksrounded.

[0090] In this embodiment, a projection and a depression relax stress inthe opposite directions. That is, as shown in FIG. 16, if the entiredisplay device (not shown) is bent in the direction shown by solid linearrows, by which a tensile stress is applied to the entire polishedsurface of the thin glass layer having the projections and depressions,a tensile stress is applied to each projection, and a compressive stressis applied to each depression. On the contrary, if the entire displaydevice (not shown) is bent in the direction shown by solid line arrowsof FIG. 17, a compressive stress is applied to each projection, and atensile stress is applied to each depression. Accordingly, as a whole,the stresses are relaxed.

[0091] Further, as schematically shown in FIG. 18, even if cracks 301are developed from flaws made during the manufacturing process after thethin glass layer 103 is shaped to have the projections and depressionthrough the mechanical polishing step and the chemical polishing step,the stress intensively applied to the tip of each crack 301 is limitedto the range of one projection and depression (as shown by an arrow inFIG. 18). Accordingly, the degree of such an intensively applied stressis considerably reduced as compared with that of the conventionaldevice. Thus, the breaking strength of the thin glass layer 103 can beconsiderably increased.

[0092] Although a PES film is used as the plastic substrate in thisembodiment, the material of the plastic substrate is not limitedthereto, but other kinds of plastic substrate can be used. For example,a polyethylene terephthalate (PET) regin film having a thickness ofabout 0.1 mm can be used. Furthermore, a polyethylene naphthalate (PEN)resin, a polyolefin resin such as a polycarbonate (PC), a cycloolefinpolymer, etc., an acrylic resin, a liquid crystal polymer, a reinforcedplastic including an inorganic material, a polyimide, etc. can also beused.

[0093] (Second Embodiment)

[0094] Next, the second embodiment of the present invention will bedescribed below. FIG. 19 is a sectional view showing an active matrixtype display device according to this embodiment. FIGS. 20 to 23 aresectional views showing steps of a method of manufacturing the activematrix type display device of this embodiment. Although two devices areshown in FIG. 19, and one device is shown in FIGS. 20 to 23, in theactual device, a great number of such devices are arranged in atwo-dimensional array. With respect to this embodiment, only thefeatures different from those of the first embodiment will be describedbelow, and the descriptions of the same features will be omitted.

[0095] In this embodiment, active matrix devices are formed on a glasssubstrate serving as a device forming substrate, and then, the thicknessof the device forming substrate is reduced to make a thin glass layer.At this time, the thickness of the areas corresponding to at least theactive elements is made thicker, and the thickness of the other areas ismade thinner. In an active matrix type display device having a deviceforming substrate, on which active elements, e.g., thin filmtransistors, are formed, multiple layers of thin films are formed in theareas where the thin film transistors are formed. Accordingly, suchareas are considered to locally receive a large stress as compared withother areas, e.g., the pixel areas, which do not have thin filmtransistors and wirings. Therefore, from the mechanical viewpoint suchas reinforcement of strength, it is preferable that the thickness of thethin glass layer is made thicker in the areas where the thin filmtransistors and wirings are formed, as compared with the other areas.Furthermore, it is also preferable that the thin glass layer serving asa block layer for blocking moisture, etc., is relatively thick so as tomaintain the chemical stability of the active layers of the thin filmtransistors.

[0096] As shown in FIG. 19, the active matrix type display device ofthis embodiment is substantially the same as that of the firstembodiment, except that the projections and depressions of the thinglass layer 103 are made thicker in a thin glass portion 401corresponding to the thin film transistors 105 and the wirings, and aremade thinner in a thin glass portion 402 corresponding to the otherareas.

[0097] Next, a method of manufacturing an active matrix type displaydevice in this embodiment will be described with reference to FIGS. 20to 23. Since the method of manufacturing an active element is the sameas that in the first embodiment, the descriptions thereof are omitted.

[0098] As shown in FIG. 20, a positive type resist 403 of, e.g., anovolac resin, having a thickness of about 5 μm is evenly applied to theback surface of the glass substrate 201, on which the thin filmtransistor 105 is formed. Then, the workpiece is exposed to a lightemitted from the side of the thin film transistor 105, with a lightintensity being sufficient to pattern the positive type resist 403.

[0099] As shown in FIG. 21, a pattern, in which only the masked resist403 is left, is formed using the thin film transistor 105 and thewirings (not shown) as masks, through the developing method. At thistime, the baking temperature can be relatively low, about 100° C., sothat the resist 403 is dissolved or peeled when the workpiece is soakedin a hydrofluoric acid solvent later.

[0100] As shown in FIG. 22, an adhesive agent, which is superior in theresistance to hydrofluoric acid, and the adhesion power of which isweakened when it is irradiated with an ultraviolet light, is coated,without any space, over the surface of the glass substrate 201 (shown inFIG. 21), which is not the side of the resist pattern 403 (shown in FIG.21). The coated adhesive agent serves as a temporary bonding agent 204.A temporary substrate 205 of a fluoroplastic sheet, which is highlyresistant to hydrofluoric acid, is provided on the temporary adhesionlayer 204 so as to support to the glass substrate 201. The surface ofthe temporary substrate 205 at the side of the temporary adhesion layer204 is coated so as to improve the adhesion properties with respect toan organic material. Then, the entire workpiece is soaked in ahydrofluoric acid solvent so that the thickness of the glass substrate201 becomes about 30 □m, to obtain a thin glass layer 103. At this time,it is preferable that after the thickness of the glass substrate 201reaches a predetermined level, ammonia, for example, is added to thehydrofluoric acid solvent so as to adjust the etching rate. Since thepatterned resist 403 does not have a sufficient resistance tohydrofluoric acid, it is peeled off a little time after the workpiece issoaked in the hydrofluoric acid solvent. In this way, the thickness ofthe thin glass portion 401 of the thin glass layer 103 corresponding tothe thin film transistor 105 becomes relatively thick, i.e., about 50□m, and the thickness of the thin glass portion 402 corresponding to theother areas becomes relatively thin, i.e., about 25 μm.

[0101] As shown in FIG. 23, an adhesion layer 102 is formed all over theetched surface of the thin glass layer 103 after the thin glass layer103 is fully cleaned. Then, a polyether sulfone resin (PES) film havinga thickness of about 0.1 mm serving as a plastic substrate 101 is bondedto the adhesion layer 102 using the vacuum laminating technique.

[0102] Thereafter, the active matrix type display device of thisembodiment is completed in the same manner as the first embodiment.

[0103] In this embodiment, the thickness of the thin glass layer is madethicker in the areas protected by the resist, corresponding to the thinfilm transistors and the wirings. This can be performed in aself-aligned manner since the start of the etching process is delayed atthese areas due to the existence of the resist. Further, in thisembodiment, it is possible to make a smooth wavy structure having thecycle unit of a thin film transistor and a wiring portion. The reasonfor this is that the projections and depressions of the thin glass layerare formed with the help of the resist in the initial stage of theetching of the glass substrate. As the etching process proceeds, theboundaries between the projections and the depressions are made smooth.For this reason, the effect of the projections and depressions explainedin the descriptions of the first embodiment can also be obtained forthis embodiment. In this embodiment, the cross-sectional shape of thethicker portions of the thin glass layer can be rounded square, roundedrectangular, trapezoid, etc. Further, the size of the projections is notnecessarily the same as the size of the device portion or the wiringportion, but can be larger or smaller.

[0104] In this embodiment, the etching selectivity is based on the softbaking of the resist. However, the etching method is not limitedthereto. For example, if the residue of the resist may cause a problem,a hard-baking of the patterned resist at a temperature of 140° C. isperformed with a certain degree of hydrofluoric acid-resistantproperties being left. Then, the glass substrate is etched for a fewtens of Elm using a hydrofluoric acid solvent containing ammonium, whichcan reduce the effect on the resist, then the resist is peeled off, andthen a further etching of the glass substrate is performed, therebyobtaining the same structure.

[0105] Furthermore, in this embodiment, the exposure step is performedafter the formation of the thin film transistor portion and the wiringportion including the signal lines and the gate lines, and the exposureis performed from the side where the thin film transistors and wiringsare formed. Accordingly, the thickness of the thin glass layer in theareas including all of such thin film transistors and wirings is madethicker. However, the present invention is not limited thereto. Forexample, in the case where the active matrix type display device shouldbe more flexible in the direction of the signal lines, if the thin glasslayer is thick in the areas directly below the signal lines, therequired flexibility of the device is inhibited. In such a case, it ispossible to form a resist pattern on the backside of the glass substratebefore the formation of the signal lines. Similarly, it is possible tomake the thin glass layer thicker in the areas corresponding only to thethin film transistors. It is preferable that the difference between thethickness of the thicker areas and the thickness of the thinner area ofthe thin glass layer is about a fifth or more and a half or less of thethickness of the thicker areas. The reason for this is the same as thatexplained in the descriptions of the first embodiment.

[0106] Furthermore, in accordance with the periodicity of the wavystructure and the characteristics of the display device, it is possibleto perform the exposure step using masks when the backside pattern isformed, as in the case of an ordinary photoetching step, to form apredetermined pattern. Further, it is possible to perform the exposurestep on the resist using masks as in the case of the ordinaryphotoetching step in order to form the projections and depressions inthe process of forming a thin glass layer having projections anddepressions with a height of a fifth or more and a half or less of thethickness of the thin glass layer, as mentioned in the descriptions ofthe first embodiment.

[0107] (Third Embodiment)

[0108] Next, the third embodiment of the present invention will bedescribed below. FIG. 24 is a sectional view showing an active matrixtype display device of this embodiment. FIGS. 27 to 29 are sectionalviews showing the steps of a method of manufacturing the active matrixtype display device according to this embodiment. Although only twodevices are shown in FIGS. 26 to 29, actually there are a great numberof such devices arranged in a two-dimensional array. The details of thethin film transistors are not shown. With respect to this embodiment,only the difference between this embodiment and the first embodimentwill be described, and the descriptions on the same features will beomitted.

[0109] In this embodiment, active elements are formed on a glasssubstrate serving as a device forming substrate. Then, the thickness ofthe device forming substrate is decreased to form a thin glass layer.Subsequently, a compressive stress applying layer is formed on thepolished surface of the thin glass layer using a material having alarger coefficient of linear expansion than the glass. Then, thecompressive stress applying layer is cooled to apply a compressivestress on the polished surface of the thin glass layer.

[0110] In many cases, a compressive stress is applied on both sides of aglass substrate, as shown in FIG. 25. The reason for this is that thedevelopment of a crack, which may lead to the breaking of glass, iscaused by a tensile stress applied to the tip of the crack. Such acompressive stress is applied to a non-alkali glass substrate which isnormally used in an active matrix type display device. When thin filmtransistors 105, etc. are formed on a glass substrate and the thicknessof the glass substrate is decreased to form a thin glass layer 103 asshown in FIG. 26, a compressive stress is applied to a side of the thinglass layer 103 on which the thin film transistors 105 are formed.However, since the thickness of the glass substrate has been decreased,a tensile stress is applied to a side of the thin glass layer 103opposite to the side on which the thin film transistors 105 are formed.Accordingly, if a crack exists on this side, it receives a tensilestress from the initial stage. If a further tensile stress is applied tothis portion by, e.g., bending the entire display device, the tip of thecrack easily receives a considerable level of tensile stress.

[0111] In order to solve this problem, the mechanical strength of thethin glass layer can be improved by forming a compressive stressapplying layer on the surface of the thin glass layer opposite to thesurface on which the thin film transistors are formed. Although it ispossible to apply a certain degree of compressive stress to that surfaceby the adhesion layer for bonding the thin glass layer and the plasticsubstrate, it is not possible to apply a great deal of compressivestress in this way. With the structure of this embodiment, even if asoft material such as an epoxy adhesive is used as the adhesion layer,it is possible to apply a compressive stress to the thin glass layerwithout being relaxed by the adhesion layer. In this case, thecompressive stress applying layer should have a coefficient of linearexpansion greater than the glass substrate, and should be cooled afterthe formation thereof to apply a compressive stress to the thin glasslayer by the shrinkage of the compressive stress applying layer.

[0112] Next, a method of manufacturing the active matrix type displaydevice according to this embodiment will be described with reference toFIGS. 27 to 29. Since the method of forming active elements in thisembodiment is the same as that in the first embodiment, the descriptionsthereof are omitted. In this embodiment, the display device is areflection type liquid crystal display device, and the compressivestress applying layer can also serve as a reflection layer.

[0113] As shown in FIG. 27, a surface of the glass substrate 201, onwhich the thin film transistors 105 are formed, is coated with anadhesive agent, which is superior in the resistance to hydrofluoricacid, and the adhesion power of which is weakened if it is irradiatedwith an ultraviolet light, so as to form a temporary adhesion layer 204.Further, a temporary substrate 205 of a fluoroplastic sheet, which ishighly resistant to hydrofluoric acid, is provided on the temporaryadhesion layer 204 so as to oppose to the glass substrate 201. Theadhesion surface of the intermediate substrate 205 is coated so as toimprove the adhesion properties with respect to an organic material.

[0114] As shown in FIG. 28, the glass substrate 201 is mechanicallypolished using a polishing agent, with the level of coarseness of thepolishing agent being adjusted, so that the thickness thereof becomesabout 0.1 mm to form the thin glass layer 103. Thereafter, the entireworkpiece is soaked in a hydrofluoric acid solvent so that the thinglass layer 103 is dissolved until the thickness thereof becomes about30 □m. It is preferable that when the thickness of the glass substratereaches a certain level, ammonia etc. is added to the hydrofluoric acidsolvent in order to adjust the etching rate. Subsequently, the workpieceis sufficiently cleaned. Then, aluminum (Al) is grown on a surface ofthe thin glass layer 103, on which the thin film transistors 105 are notformed, i.e., the etched surface, through the sputtering method untilthe thickness thereof becomes about 100 nm. This aluminum layer servesas a compressive stress applying layer 501. At this time, the substratetemperature is set to be at 100° C.

[0115] Then, an adhesion layer 102 is formed all over the compressivestress applying layer 501 using an adhesive agent superior in theadhesion properties. Subsequently, a polyethersulfone resin (PES) filmhaving a thickness of about 0.1 mm and serving as the plastic substrate101 is bonded to the adhesion layer 102 using the vacuum laminatingtechnique. At this time, the temperature is maintained to be about 100°C.

[0116] Then, as shown in FIG. 29, the temperature is lowered to anambient temperature (e.g., 23° C.) at a temperature lowering rate ofabout 10° C./min. Normally, there is over an order of magnitudedifference between the coefficient of linear expansion of glass and thatof aluminum. For example, for many glass substrates, the coefficient oflinear expansion is on the order of 10⁻⁷/° C., while the coefficient oflinear expansion of aluminum is on the order of 2×10⁻⁵/° C. Accordingly,as shown by arrows in FIG. 29, in the temperature lowering processperformed after the formation of the compressive stress applying layer501, a compressive stress is applied to the thin glass layer 103 fromthe side of the compressive stress applying layer since the compressivestress applying layer 501 shrinks in the temperature lowering process,while the thin glass layer 103 does not shrink very much.

[0117] Thereafter, the active matrix type display device according tothis embodiment is completed in the same manner as the first embodiment.

[0118] In this embodiment, a phenomenon may occur that the entire activematrix substrate is warped due to the stress relaxation during thetemperature lowering process which is performed after the thin glasslayer and the plastic substrate are bonded. It is possible to preventthis phenomenon by inserting the active matrix substrate between twoglass substrates each having a thickness of about 1.1 mm, and having asmooth surfaces, and then lowering the temperature.

[0119] Further, in this embodiment, it is possible to prevent thegeneration a tensile stress that may develop a crack even at thebackside of the thin glass layer, on which no compressive stress hasbeen applied, by forming a compressive stress applying layer on thesurface of the thin glass layer contacting the adhesion layer.

[0120] Since the display device in this embodiment is a reflection typeliquid crystal display device, aluminum is used to form the compressivestress applying layer. However, the material of the compressive stressapplying layer is not limited to aluminum, but any material having alarger coefficient of linear expansion than glass, such as silver,molybdenum, copper, an alloy including any of aluminum, silver,molybdenum, and copper, can be used. Further, the deposition method isnot limited to the sputtering method, but can be the chemical depositionmethod, etc. It should be noted, however, that since a compressivestress caused by the difference between coefficients of linear expansionshould be applied to the surface of the thin glass layer, the selecteddeposition method should allow a heat treatment at a temperature of,e.g., about 150° C., which may not cause damage to the thin glass layer.Moreover, although a metal material, which does not have lighttransmission properties, is used as the material of the compressivestress applying layer in this embodiment, there is a case where a lighttransparent material should be used, as in the case of a transparentliquid crystal display device. The present invention can be employedeven in such a case by depositing a glass material having a largercoefficient of linear expansion than the thin glass layer by using,e.g., the RF sputtering method. For example, if an alumino-boro silicateglass material is used to form a device forming substrate, a lead glassusing lead-potassium-sodium silicate or soda-lime glass having a largecoefficient of linear expansion can be used as the compressive stressapplying layer. Since there is no high-temperature processing orchemical processing after the formation of the compressive stressapplying layer, there is no problem even if a lead glass or a soda limeglass, which does not have good heatproof or chemical-proof properties,is used.

[0121] (Fourth Embodiment)

[0122] Next, the fourth embodiment of the present invention will bedescribed. FIG. 30 is a sectional view showing an active matrix typedisplay device of this embodiment. Although only two devices are shownin FIG. 30, actually there are a great number of such devices arrangedin a two-dimensional array. Further, the details of the active elementsare omitted. With respect to this embodiment, only the features that thefirst embodiment does not have will be described, and the descriptionsof the same features will be omitted.

[0123] In this embodiment, there is provided a hydroxyl group blockinglayer for blocking the soakage of molecules having hydroxyl groups,which exist on the surface of the thin glass layer at the adhesion layerside bonded to the plastic substrate, and may help the development ofcracks. As mentioned in the descriptions of the first embodiment, thereis provided on the active element side of the thin glass layer anundercoat layer such as a silicon oxide layer for preventing the traceof alkali elements etc. from seeping from the glass substrate. Thisundercoat layer also works to prevent the soakage of molecules havinghydroxyl radicals from the active element side. However, on the surfaceof the polished surface of the thin glass layer, there is no such layerto prevent the soakage of molecules having hydroxyl radicals into cracksexisting. Accordingly, molecules having hydroxyl groups contained in themoisture in the atmosphere air or the adhesion layer may easily reachthe tips of cracks, thereby advancing the development of the cracks,which may lead to the breaking of the glass. Accordingly, if a layer forpreventing the soakage of molecules having hydroxyl groups into thepolished surface of the thin glass layer is employed, the strength ofthe glass layer may be considerably improved.

[0124] As shown in FIG. 30, the active matrix type display device ofthis embodiment does not have projections and depressions on the thinglass layer 103, as in the case of the first embodiment. Alternatively,there is provided a hydroxyl group blocking layer 601 between the thinglass layer 103 and the adhesion layer 102.

[0125] A method of manufacturing an active matrix type display deviceaccording to this embodiment differs from the first embodiment in thatafter the thickness of the glass substrate is decreased to form the thinglass layer 103, no projection nor depression is formed thereon, unlikethe first embodiment, but a hydroxyl group blocking layer 601 is formedby applying a silane coupling agent such asdichlorohydroxypropyltrimetylsilane to the polished surface of theglass, and heat-treating the workpiece at a relatively low temperature,such as 70° C., for about an hour. FIG. 31 shows a chemical formula thatcan be applied to the silane coupling agent of this embodiment.

[0126] Since the hydroxyl group blocking layer 601 is provided on thethin glass layer 103, oxygen atoms and hydrogen atoms of the silanecoupling agent form hydrogen bonds in the hydroxyl group blocking layer601 provided at the polished surface side of the thin glass layer 103.Accordingly, there exist alkyl groups on the surface of the hydroxylgroup blocking layer 601, which prevent the soakage of molecules havinghydroxyl groups.

[0127] The material of the hydroxyl group blocking layer 601 can be asilane coupling agent, preferably a material including at least one of3-glycidoxylpropyl-trimethoxysilane,3-[(methacryloyloxy)propyl]-trimethoxysilan,N-[3-(trimethoxysilyl)propyl]-ethlenediamine, and3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoroctyl-trimethoxysilane

[0128] Further, not only an organic material such as a silane couplingagent but also an inorganic material can be used to form the hydroxylgroup blocking agent 601. For example, it is possible to applypolysilazane dissolved in xylene to the polished surface of the thinglass layer 103 by the spin coating method, and to heat treat theworkpiece in the atmosphere air at a temperature of 200° C. for aboutthree hours, thereby forming a silicon oxide layer having a thickness ofabout 100 nm on the surface of the thin glass layer 103. The siliconoxide layer thus formed can serve as a layer for preventing hydroxylgroups from reaching the polished glass surface. Further, since the spincoating method is used in the deposition step, cracks and flaws, if any,of the polished glass surface can be protected.

[0129] (Fifth Embodiment)

[0130] Next, the fifth embodiment of the present invention will bedescribed below. FIG. 32 shows a sectional view of an active matrix typedisplay device according to this embodiment. Although only two devicesare shown in FIG. 32, actually there are a great number of such devicesarranged in a two-dimensional array. Further, the details of activeelements are omitted. With respect to this embodiment, only the featureswhich are different from the feature of the first embodiment will bedescribed, and the descriptions of the same features will be omitted.

[0131] In this embodiment, a reinforcing member 701 having a meshstructure is provided in the adhesion layer 102. It is preferable thatthe reinforcing member 701 is provided directly below the active element105 in the adhesion layer 102. In this way, it is possible to reinforcethe thin glass layer 103 in the area where the active element 105 isformed, which has a relatively large residual stress, and thus isrelatively weakened. Accordingly, it is possible to considerably improvethe strength of the thin glass layer 103.

[0132] As shown in FIG. 32, the active matrix type display device ofthis embodiment does not include projections and depressions on the thinglass layer 103, unlike the first embodiment, but does include areinforcing member 701 having a mesh structure in the adhesion layer102.

[0133] The above-described embodiments can be combined to gain combinedeffects. For example, as the result of the combination of the first andthird embodiments, it is possible to further improve the strength of thepolished glass layer by the effect of having projections and depressionsin the first embodiment, and the effect of preventing the entry ofmolecules having hydroxyl groups of the third embodiment. Thecombination is not limited to the first and third embodiments, but anycombination of the above-described embodiments is possible.

[0134] Although the cases of a liquid crystal display device have beendescribed relating to the above-described embodiments, the presentinvention is not limited to liquid crystal display devices, but can beapplied to any devices requiring matrix driving. For example, thepresent invention can be applied to a self-luminance type display devicesuch as an organic electroluminescence display, a display usingelectrophoresis devices. Further, if liquid crystal is used, theopposing electrode can be eliminated, a pair of comb-shaped pixelelectrodes can be provided at the device circuit regions side, and anelectric filed can be applied in the direction of display in order todrive the liquid crystal. If organic electroluminescence is used for thedisplay, it is preferable that a peripheral driver circuit of currentdriving type is provided, and a pixel includes a selection switchcomposed of two to six transistors, a current supply purpose drivingtransistor, and a transistor property fluctuation correction circuit.These circuits can be conventionally-used circuits. Further, a pluralityof thin film transistors can be used as active elements.

[0135] As described in detail, according to the present invention, evenif a glass substrate is used as a device forming substrate, it ispossible to provide an active matrix type display device, which isreliable and flexible as a whole, and a method of manufacturing thesame.

[0136] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concepts as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. An active matrix type display device comprising:a first substrate, which is flexible; a thin glass layer provided on thefirst substrate via an adhesion layer, and having projections anddepressions on a surface thereof opposing to the first substrate, theprojections and depressions having rounded tips and bottoms; activeelements provided on the thin glass layer, each active elementcorresponding to a pixel; a display provided above the thin glass layer,and driven by the active elements to display an image pixel by pixel;and a second substrate provided on the display, and having an opposingelectrode formed thereon.
 2. The active matrix type display deviceaccording to claim 1, wherein a height of the projections anddepressions is a fiftieth or more and a half or less of a thickness ofthe thin glass layer.
 3. The active matrix type display device accordingto claim 1, wherein the first substrate is formed of a plastic.
 4. Anactive matrix type display device comprising: a first substrate, whichis flexible; a thin glass layer provided on the first substrate via anadhesion layer; active elements provided on the thin glass layer, eachactive element corresponding to a pixel; a display provided above thethin glass layer, and driven by the active elements to display an imagepixel by pixel; and a second substrate provided on the display, andhaving an opposing electrode formed thereon, a thickness of the thinglass layer in regions corresponding to the active elements beingthicker than a thickness of other regions.
 5. The active matrix typedisplay device according to claim 4, wherein the first substrate isformed of a plastic.
 6. An active matrix type display device comprising:a first substrate, which is flexible; a thin glass layer provided on thefirst substrate via an adhesion layer; a compressive stress applyinglayer provided between the adhesion layer and the thin glass layer, thecompressive stress applying layer applying a compressive stress to asurface of the thin glass layer at a side of the adhesion layer; activeelements provided on the thin glass layer, each active elementcorresponding to a pixel; a display provided above the thin glass layer,and driven by the active elements to display an image pixel by pixel;and a second substrate provided on the display, and having an opposingelectrode formed thereon.
 7. The active matrix type display deviceaccording to claim 6, wherein a coefficient of linear expansion of thecompressive stress applying layer is larger than a coefficient of linearexpansion of the thin glass layer.
 8. The active matrix type displaydevice according to claim 7, wherein the compressive stress applyinglayer is formed of a material selected form the group consisting ofaluminum, silver, molybdenum, copper, and an alloy containing any ofaluminum, silver, molybdenum, and copper.
 9. The active matrix typedisplay device according to claim 7, wherein the compressive stressapplying layer is formed of a material selected from a group consistingof lead glass and soda-lime glass.
 10. The active matrix type displaydevice according to claim 6, wherein the first substrate is formed of aplastic.
 11. An active matrix type display device comprising: a firstsubstrate, which is flexible; a thin glass layer provided on the firstsubstrate via an adhesion layer; a hydroxyl group blocking layerprovided between the adhesion layer and the thin glass layer, andpreventing an entry of a hydroxyl group; active elements provided on thethin glass layer, each active element corresponding to a pixel; adisplay provided above the thin glass layer, and driven by the activeelements to display an image pixel by pixel; and a second substrateprovided on the display, and having an opposing electrode formedthereon.
 12. The active matrix type display device according to claim11, wherein the hydroxyl group blocking layer containing a silanecoupling agent.
 13. The active matrix type display device according toclaim 11, wherein the first substrate is formed of a plastic.
 14. Anactive matrix type display device comprising: a first substrate, whichis flexible; a thin glass layer provided on the first substrate via anadhesion layer; active elements provided on the thin glass layer, eachactive element corresponding to a pixel; a display provided above thethin glass layer, and driven by the active elements to display an imagepixel by pixel; a second substrate provided on the display, and havingan opposing electrode formed thereon; and a reinforcing member having amesh structure, provided in the adhesion layer.
 15. The active matrixtype display device according to claim 14, wherein the reinforcingmember is at least provided in regions corresponding to the activeelements.
 16. The active matrix type display device according to claim14, wherein the first substrate is formed of a plastic.
 17. A method ofmanufacturing an active matrix type display device, the methodcomprising: forming active elements each corresponding to a pixel on adevice forming substrate of glass; polishing the device formingsubstrate to make it thinner by first performing a mechanical polishing,and then performing a chemical polishing; bonding a surface of thedevice forming substrate, which has been polished, to a plasticsubstrate via an adhesion layer; and forming a display driven by theactive elements to display an image pixel by pixel, by placing a countersubstrate so as to oppose to the device forming substrate.
 18. A methodof manufacturing an active matrix type display device, the methodcomprising: forming active elements each corresponding to a pixel on adevice forming substrate of glass; polishing the device formingsubstrate to make it thinner; forming a compressive stress applyinglayer on a polished surface of the device forming substrate, acoefficient of linear expansion of the compressive stress applying layerbeing larger than a coefficient of linear expansion of the deviceforming substrate, and then cooling the compressive stress applyinglayer; bonding a plastic substrate to a surface of the device forminglayer via an adhesion layer, on which the compressive stress applyinglayer is formed; and forming a display driven by the active elements todisplay an image pixel by pixel, by placing a counter substrate so as tooppose to the device forming substrate.